Phantom odors have always been tied to hauntings and ghost stories. Before sophisticated equipment could measure EMF and voice recorders were picking up EVPs, personal stories of encounters with the supernatural nearly always came accompanied with a particular odor. Even today, part of our investigator's interview questionnaire always include questions about phantom odors, and any personal experiences involving such are carefully documented.
But why are we so interested in phantom odors?
Many believe that phantom odors are an excellent way for an entity to communicate with the living. It presumably takes less energy to manifest a scent than to manifest as a visual apparition, make a noise, or move an object in our realm. Certain scents can also help identify an entity, such as a loved one's favorite perfume or the unmistakable scent of a pipe smoker's tobacco.
Certain scents may also even help a witness distinguish what KIND of paranormal entity they are dealing with. According to folklore, some entities manifest a rather set array of phantom smells. For example, demonic or evil entities are believed to make their presence known with a foul smell, such as sulfur, rotting flesh, and even feces. Marian apparitions, or visions of the Virgin Mary and other saintly or religious figures are said to give off an odor of fresh roses. And of course, the entities of once living human beings tend to give off very human smells, such as a favorite cologne or perfume, cooking smells, and the smells associated with favorite smoking devices.
To me, it does make sense that an entity would use scent to make its presence known, as scent is the human sense most strongly linked to recall memory. Smells can evoke emotions and bring up memories in a way that other senses simply cannot. However, it is extremely important to note that like all senses, the sense of smell is not infallible, and all natural causes must be ruled out before a phantom smell is classified in the paranormal realm.
According to Dr. Hoffman of the Medical Consumer's Advocate, smell is a chemical sense. That means, when you smell something, your brain is perceiving specific airborne molecules. These molecules bind to receptors in the olfactory epithelium, which is the tissue that lines the back of the roof of the nasal cavity. Nerve impulses are generated, which travel first to the olfactory bulb, then to other areas deeper within the brain. That means, there's a lot of places where things can go wrong along the way...
In the medical world, the term for phantom smell is phantosmia. Some phantom smells are simply hallucinations, plain and simple, brought on by any number of psychiatric disorders, including schizophrenia. We generally tend to think of hallucinations only being visible in nature, but any sense can be affected by these psychiatric hallucinations.
That said, smelling something that is not there doesn't automatically point to a psychiatric disorder. Physiological issues are more often the culprit when it comes to phantom smells. Damage to the brain and anywhere along the "smell route" as a result from sinus infections, injury, medications, dental issues, brain tumor, or temporal lobe epilepsy can cause phantom smells. Migraine sufferers will often report phantom smells, the more popular being coffee and smoke, right before a migraine, and those with temporal lobe epilepsy sometimes report similar right before an episode. As it is theorized that phantom smells can stem from issues from both the smell receptors AND the central nervous system, any experiences with phantom smells should be well documented and reported to a doctor as soon as possible.
There's also another facet to the long list of dysosmias (olfactory disorders) that can be mistaken for paranormal activity: parosmia. Parosmia is a distortion of smell. Not as common as phantom smells, parosmia is still something that must be taken into consideration whenever a certain odor is associated with a haunting. The main reason for this is because of a horrible sub-category of parosmia called cacosmia, where the person will smell fecal matter in place of another smell. Since foul odors are associated with negative hauntings, falsely smelling a foul odor may cause a bias in perception.
Dysosmias, including, but not limited to, parosmia and phantosmia aren't the only natural explanations for alleged phantom smells of a paranormal nature. Scent ions are strange little things...they can become trapped in fabrics, masonry, and even wood surfaces to be released months, and even years later with the right change of humidity, temperature, or barometric pressure. Scent ions also travel in ways that may not make a lot of sense at first. One major false positive that I've personally experienced is foul odors coming from drains, and even toilets in homes where the water has been turned off. Neighborhoods and apartment buildings are also exceptionally vulnerable to false phantom smells coming from other locations.
So if phantom smells are a part of your suspected haunting, keep a few things in mind:
1. Get confirmation from another, unbiased source that there IS in fact a smell
2. Document each event
3. GET A MEDICAL EVALUATION
4. Rule out natural explanations
5. Read Theresa's Haunted History of the Tri-State for more information!
UPDATE April 2014: Here's a wonderful article explaining the science behind the link between smells and memory: